Rechargeable batteries manufactured from laminates of solid polymer electrolytes and sheet-like electrodes display many advantages over conventional liquid electrolyte batteries. These advantages include: lower overall battery weight, high power density, high specific energy, and longer service life. In addition, they are more environmentally friendly since the danger of spilling toxic liquid into the environment is eliminated.
Solid polymer cell components typically include positive electrodes (also referred to as cathodes), negative electrodes (also referred to as anodes), and a separator material capable of permitting ionic conductivity, such as a solid polymer electrolyte, sandwiched therebetween. Moreover, a current collector can also be associated with either one of the electrodes, especially the cathode.
Typical electrochemical generators comprise a plurality of individual electrochemical cells stacked or bunched together to form a battery. The electrochemical cells may be of a mono-face configuration or a bi-face configuration. As illustrated in FIG. 1, an electrochemical cell 10 having a mono-face configuration is a laminate including a current collector 18, a cathode 16, an electrolyte separator 14, and an anode 12, which is covered with an insulating polypropylene film 15 to insulate the electrochemical cell from an adjacent electrochemical cell in order to prevent short circuits. The current collector 18 is typically a 15–25 μm thick carbon coated aluminum foil; the cathode layer 16 is typically a 10–100 μm thick composite; the electrolyte separator 14 is typically a 20–80 μm thick polymer and alkali metal salt layer; the anode layer 12 is typically a lithium or lithium alloy metal foil 15–80 μm thick; and the polypropylene film 15 is typically 12–26 μm thick.
As illustrated in FIG. 2, an electrochemical cell 20 having a bi-face configuration is a laminate including a central current collector 18 having a cathode 16 on both of its sides, an electrolyte separator 14 adjacent each cathode 16, and an anode 12 adjacent each electrolyte separator 14. The typical thickness of each of the components is similar to that of the mono-face cell laminate previously described. In a bi-face configuration, the insulating polypropylene film is eliminated since the anode of a first cell is not adjacent to the cathode of a second cell and therefore cannot short circuit directly.
As illustrated in FIGS. 1 and 2, the thin film anodes 12 and cathodes 16 are laminated in an offset pattern, the anodes 12 protruding on one side of the laminate and the cathode current collectors 18 protruding on the other side of the laminate such that when a series of laminates are stacked into an electrochemical cell, all protruding anodes 12 can be connected together and all protruding cathode current collectors 18 can be connected together. The electrolyte separator 14 is positioned and sized in such a manner that it completely separates the anodes from the cathodes to prevent short circuiting between the two.
One manufacturing process consists in laminating the thin films of anode, electrolyte separator, cathode and cathode current collector into mono-face or bi-face configurations using a continuous manufacturing process and cutting the laminates to size prior to stacking. The laminates are cut perpendicular to their longitudinal axis. The cutting operation is delicate because it exposes the edges of each layer of the laminate; the electrolyte separator no longer extending beyond the anode layer and the cathode current collector layer to ensure adequate electrical insulation. Furthermore, the cutting operation may cause burring of the anode layers or of the current collector with the effect that the burred metal edges may extend over the electrolyte separator and contact the opposite anode or cathode thereby causing a short circuit which renders the laminate unusable. At the very least, the cutting operation results in the precarious situation of having the exposed edges of the anode and cathode/current collector layers only 15–25 μm apart; any mechanical deformation of any of the layers (anode, cathode, current collector and separator) potentially causing a short circuit. Since there may be variations in the volume (e.g., the thickness) of the laminate, and specifically that of the the cathode, in the charge and discharge modes of the battery, leaving the exposed edges of the laminates unattended represents a risk of future short circuit.
Another manufacturing process consists in stacking previously cut thin films of anode and previously cut mono-face or bi-face half-cells comprising a current collector, cathode and electrolyte separator. Again, the cutting operations may have caused burring of the edges of the anode films and/or of the metal current collector foil causing the burred metal edges to extend over the electrolyte separator after lamination into electrochemical cells potentially resulting in short circuits.
Once the various layers of the laminates are stacked to form an electrochemical cell bundle, the ends of the electrochemical cell bundle are a series of freshly cut and exposed anode, separator and cathode edges which can easily cause short circuits during assembly of the electrochemical generator or later on when the generator is put into service.
Thus there is a need in the manufacturing of electrochemical generators and bundles, for a process and apparatus for preventing short circuits between the edges of the various layers of an electrochemical cell laminate or laminates.